Flat, flexible, multiple conductor, tuned-impedance electrical cables and transmission lines, such as those shown in U.S. Pat. No. 3,612,744 to Thomas and U.S. Pat. No. 4,441,088 to Anderson have been known and used for many years. Recently they have been proposed for use in testing microelectronic devices and circuits as a means for communicating high frequency, high density electrical signals along a tuned-impedance transmission line to such devices and circuits under test from test equipment located outside a test chamber. Such use is discussed in IBM Technical Disclosure Bulletin, Vol. 34, No. 2, July 1991 and in the publication entitled "High Frequency/High Density/High Vacuum Transmission Line Interface" by S. N. Argyrakis, one of the inventors in the present application, published Feb. 19, 1991 in CONNECTION TECHNOLOGY. For many such uses, Applicants have found that it is desirable to have large numbers of signal-carrying conductors in such cables, for example, approximately 900 conductors. Although it is possible to build cables of the type heretofore described with that number of conductors, Applicants have recognized that in certain applications, such cables may not have the degree of flexibility required. In particular, Applicants have recognized that in certain instances, it is desirable to route such cables along paths defined by existing service conduits. Applicants have recognized that a need exists for a flat, flexible, multiple conductor, tuned-impedance electrical cable having a large number of signal-carrying conductors which can meet the above requirements.